铀裂变瞬发中子测井与铀定量分层解释的基础研究

According the principle of high-energy neutron bombarding the underground substances, making them scattering, capture, activating, fission and inducing secondary radioactive rays, detecting the decay time spectrum from native/secondary neutrons, or energy spectrum from prompt/delayed secondary radioactive ray, many of the new technology of neutron logging can be researched and developed for mineral exploration. Compare with the natural gamma logging measuring uranium content indirectly (required chemical analysis of core-samples), Uranium fission prompt neutron logging which controlled by U.S. and Europe nuclear powers, can measuring uranium content directly (however it being restricted exports to China), and it belong in a advanced method for uranium determination. This method uses a pulsed neutron source, emitting native neutrons bombarding the drilling-hole materials and formation-rock, inducing 235U fission and sending out prompt neutrons. By detecting those prompt neutrons the uranium determination can be realized. In this respect, the project content: .(1) To study the decay time spectrum and its variation of low-energy neutrons slowing down from native neutrons and uranium fission neutrons; .(2) To study the method and influencing factors of extracting uranium fission information from the decay time spectrum of neutron;.(3) To study the principle of spatial distribution of uranium fission neutrons and uranium determination rapid algorithm; .(4) To study the subdivision interpretation method for uranium determination, and the correction technology of influencing factors..The objectives of project research: to break through the US-European technology blockade; to innovate extracting method of uranium information in deep deposits; to promote uranium fission prompt neutron logging method become a practical method in China and abandoning the method of natural gamma logging for uranium quantitative.

依据高能中子轰击井下物质，使其发生散射、俘获、活化、裂变并诱发次生射线，探测原生/次生的中子衰减时间谱，或瞬发/缓发的次生射线能谱，可研发矿产勘查的中子测井诸方法。相比间接测铀的自然γ测井(须岩芯化学分析修正铀定量)，被美欧核大国掌控的铀裂变瞬发中子测井可直接测铀(但限制仪器出口到我国)，属先进铀定量方法。该方法利用脉冲中子源发射原生中子，轰击钻孔物质与地层岩石，诱发235Ｕ裂变并放射瞬发中子，探测该瞬发中子可实现铀定量。为此，项目研究内容为：①研究原生中子与铀裂变瞬发中子慢化的低能中子衰减时间谱及变化规律；②研究从该中子衰减时间谱中提取铀裂变信息的方法及影响因素；③研究铀裂变的空间分布规律及铀定量快速算法；④研究层状铀矿的分层解释方法及影响因素修正技术。项目研究目标为：突破美欧技术封锁，创新深部铀矿床含矿信息的提取方法，促使铀裂变瞬发中子测井成为我国实用方法，以摒弃自然γ测井的铀定量。

我国为“贫铀/少铀”国家，国内铀供给仅能保障国防军工、难以支撑核能发电。然而，我国深部铀矿主要通过钻探来获取钻孔岩样，以化学分析为基础来建立铀矿勘查技术体系，造成了“取芯钻探效率低、元素分析周期长、勘查定量成本高”等固有缺点。本重点基金项目以“研发出可取代钻孔岩样化学分析的铀矿定量方法，以及开创出无需钻孔岩样化学分析的快速铀矿勘查技术体系”为主要研究目标。通过五年探索，创立了仅由钻孔测井结果圈定深部铀矿边界、确定矿产元素含量的铀矿定量方法理论，依此为研制配套测井仪器装备与计量标准装置等关键技术奠定了理论基础。. 岩矿石含有微量铀是基本事实(铀含量≥0.01%可变成铀矿)，如果沿钻孔以脉冲方式向地层发射原生中子，就能诱发岩矿石中的铀发生裂变反应并放出瞬发中子。本重点基金项目通过探测原生中子和瞬发中子，在国内率先建立并研发出直接测铀的裂变中子测井基础理论和铀矿定量方法，具体包括：首创了岩矿层内铀裂变的瞬发中子输运理论，研发出深部矿层含铀信息的提取方法，发明了基于超热中子与热中子时间谱比值的铀裂变瞬发中子测井方法，研发出可细分薄矿层的铀矿定量算法和影响因素修正技术，申请或授权了该类方法技术的首批中国专利，已形成我国首部《裂变中子测井仪》的行业标准，打破了类似技术仅由美俄掌控与封锁，为取代钻孔岩样化学分析实现无岩芯钻探，进而大幅提升钻探效率、降低勘查成本提供了前提条件，也为地浸采铀钻孔估算剩余铀量的世界难题提交了解决方案；一旦将中子测井与γ测井融合为低成本铀矿测井，就更利于推广并成为我国铀矿定量的新标准方法。综上所述，本重点基金项目取得了多项开创性成果，具有较高的学术意义和重要的实用价值。